1. Technical Field
The present invention relates to the extraction of essential oils from plants. More particularly, the present invention relates to an improved process for the hydrodistillation of essential peppermint and spearmint oils from plant material.
2. Background
Oils harvested from plant sources are known as essential oils. Peppermint and spearmint are two such essential oils of significant commercial value. These oils are used in a wide variety of applications, from flavorings in food products to personal hygiene products, additives, and scent masking products. Worldwide demand for peppermint and spearmint oil products is increasing rapidly.
Peppermint and spearmint oils, generically referred to as mint oil, are comprised of a number of constituents. These components include, but are not limited to, pulegone, mentholfuran, limonene, menthone, menthofuran, menthol, menthyl acetate and a number of ester fractions.
TABLE 1 ______________________________________ Constituents of Peppermint Oil Percentage ______________________________________ Menthol 43.18% Menthone 20.48% Menthol Acetate 5.02% 1,8 Cineole 4.80% Neomenthol 3.34% ______________________________________ *Balance made up of more than 20 other compounds.
TABLE II ______________________________________ Major Components of Spearmint Oil Percentage ______________________________________ 1-Carvone 64.82% Limonene 17.94% 3-Octanol 1.78% 1,8 Cineole 1.45% Menthone 1.35% ______________________________________ *Balance made up of more than 20 other compounds.
Each of these fractional components has a different commercial value and affects the color and taste of the oil. For example, pulegone is a known carcinogen that decreases the commercial value of the mint oil and is removed during reprocessing. Both fractional makeup and yield of mint oil vary significantly from location to location and batch to batch, depending on a number of factors, including weather, latitude, temperature conditions, soil conditions, sunlight, day length, leaf dimension, and other factors.
The batch process by which mint oil is commonly extracted from the plant is as follows: The mint plant is mowed and left to dry or cure in the field for a period of approximately two days. The mint hay is then mechanically chopped and blown into large distillation vats or tubs. Once the vats are full of chopped mint hay, they are ready for hydrodistillation.
Hydrodistillation is accomplished by introducing pressurized steam into the vat. The steam is directed through numerous small openings in the floor of the vat. From the openings, the steam passes through the chopped mint hay and is collected at the top of the vat. The steam is then routed through a return line to a condensation and separation apparatus. Steam and mint oil are condensed and collected from the condensing coil into a separation tank.
Within the separation tank the condensate separates into mint oil and water. Because of density differences, the mint oil rises to the top and the water sinks to the bottom of the separator. The mint oil is skimmed from the top of the separator and collected into storage containers, typically 55 gallon drums, for transportation and shipping. Water is drawn from the bottom of the separation tank and is further reprocessed by boiling in a reboiler. The vapor from the reboiler is then collected and condensed to collect additional mint oil.
The remaining water drawn from the bottom of the separation tank is reintroduced into the boiler to be processed into steam and fed back into the hydrodistillation loop. Each vat is typically processed by hydrodistillation for between 2 to 21/2 hours.
The site and equipment required for hydrodistillation of mint oil represents a considerable capital investment. For this reason, it is common for one mint farmer to erect a hydrodistillation facility which is then cooperatively utilized by numerous farmers in the surrounding area. At harvest time, the mint growers will process on a cooperative basis.
Hydrodistillation is effective at extracting the majority of mint oil from chopped mint hay. Using the batch method as just described, all of the constituent components that make up the mint oil, desirable and undesirable, are collected. As bulk mint oil is collected in each batch process, it is combined in storage barrels for transportation. An undesirable result is unpredictable and non-uniform analysis results for each barrel of oil produced.
The essential mint oil produced by growers is purchased by mint oil brokers. The brokers reprocess the mint oil to selectively improve the quality and grade of mint oil for various intended uses. Reprocessing is expensive and reduces the original yields. Shrinkage losses in reprocessing range from 1% to 30%. Two important goals in reprocessing are to remove undesirable fractional components and to improve clarity.
The price and demand for bulk mint oil are regulated in the mint oil industry via cooperative efforts. Thus, the price growers receive for mint oil is primarily based on sample analyses from each barrel and current set price levels. Two important empirical qualities that impact price are quality and clarity.
What is needed is a process for harvesting mint oil that improves the quality and economic value of oil and is simple and economical to implement. Such an improved process would allow the producer to improve the quality and efficiency of the mint oil distillation process, thereby reducing the need for reprocessing and the associated shrinkage and economic loss.
It is an objective of the present invention to reduce or eliminate the need for reprocessing of mint oil by providing a higher quality raw product utilizing existing equipment.
It is another objective of the present invention to control the collection of the carcinogenic fractional components of spearmint and peppermint oils, thus further reducing the need for reprocessing and the associated shrinkage in yield.
It is a further objective of the present invention to provide a means for improving the control over the fractional composition of the mint oil and to improve product clarity.
It is an objective of the present invention to provide these quality and economic advantages, as well as other advantages utilizing existing equipment or requiring minimum retooling.
These and further objectives of the present invention will become readily apparent to one skilled in the art from the following detailed description and drawings.